1. Field of the Invention
The invention relates to a screening machine for superfine powder, and more particularly to a screening machine having bi-directional airflow for superfine powder.
2. Description of the Related Art
Powder technology is one of the most important basic technologies in high and new technology industries and pharmaceutical industries in recent years. The superfine-treatment of powder changes a lot of the original properties of material, thus the application range of traditional materials is extended, and the application value of products is promoted. Therefore, improving the powder classification technology is of great importance. The powder separation and classification equipment is developing rapidly in recent years, and currently, there are two main commonly-used types: classification with a mesh screen, and classification without a mesh screen. The air screening method is a more advanced classification method, and the biggest advantage of an air screening machine is using a screen mesh for effective separation under the impact of air carried with powder, however, the shortage is that the micron-size materials with light weight and small particle size are accumulated on the mesh screen during classification to form caking to block the mesh screen, thus the screening operation cannot be performed. Although the conventional micron-size powder material air screening device adopts the principle of circulating dual airflow, the middle part of the mesh screen is easily blocked due to the uneven reverse airflow, the area of the mesh screen is small under the same volume, the air screening device is not suitable for large-scale production, and meanwhile, the air screening device is complicated in structure and high in energy consumption. At present, the commonly-used turbine classifier is mainly suitable for the materials with monomer component, for example, the large-scale production of mineral superfine powder, however, it's not suitable for the mixed powder with complicated component, for example, the screening production of plant superfine powder with high difference in specific gravity of various components, because the maximum particle size is not easy to be controlled accurately.